This invention relates generally to synchronous machines and, more particularly, to synchronous machines with High Temperature Superconducting rotors.
A synchronous machine typically includes a motor housing, a stator including a plurality of armature windings mounted between a plurality of stator teeth, and a rotor assembly. The rotor assembly includes a rotor core and a rotor shaft extending through the rotor core. The rotor core can be either a salient pole or a cylindrical configuration, and includes a plurality of field windings mounted thereon. The motor housing includes at least one endshield and houses at least a portion of the rotor assembly. Synchronous machines also typically include at least one bearing sized to receive and support the rotor shaft, and at least one inner bearing cap separated from the bearing. Typically, the bearing is positioned between an endshield and an inner bearing cap and facilitates rotation of the rotor shaft when the armature windings are energized.
Recent technological advances have allowed synchronous machines to utilize HTS (high temperature superconducting) ceramic field windings in lieu of conventional copper windings. The HTS windings typically are fabricated from bismuth-2223 ((Bi,Pb)2Sr2Ca2Cu3O10) and are loaded with significantly larger currents than conventional copper windings can sustain. Therefore, machines with HTS windings can generate more powerful magnetic fields in a given volume of space compared to machines with conventional windings. Currently, a cryogenically cooled superconducting machine utilizing a toothless stator winding is able to match the power output of an equally rated conventional machine with as little as one-third the size and weight of the conventional machine.
In a known machine with HTS windings, there are permeance variations in the stator due to the use of conventional slotted magnetic metal cores that generate varying forces in the air gap. The varying air gap forces can produce noise by exciting the machine""s structure and the torque is limited by the need to provide space for the teeth structure. However, there are many applications where motor noise is undesirable and small size is important, such as, for example, in a submarine.
Accordingly, it would be desirable to facilitate a reduction in permeance variations and increase torque (power) density in a stator of a synchronous machine with HTS field windings.
The present invention is, in one aspect, a machine in which a stator is fabricated such that the teeth of the stator are of a non-magnetic material. Since the teeth are non-magnetic, the teeth do not contribute to generation of noise due to variations in magnetic fields, as do the magnetic teeth in known stators. Specifically, the non-magnetic teeth facilitate a reduction of permeance variations induced by a plurality of stator windings mounted on the stator teeth, thereby lessening variations in the air gap forces between a rotor and the stator. Additionally, utilizing non-magnetic teeth allows for the use of additional windings embedded in the non-magnetic teeth to increase current density and torque. Accordingly, noise caused by the variations in air gap forces is reduced and torque is increased.